1. Field of the Invention
The present invention relates generally to cranes for use in environments such as encountered in a boiling water nuclear reactor (BWR). More specifically, the present invention relates to a water proof cover arrangement for a heavy-duty overhead crane which prevents crane components from becoming radioactively contaminated when lowered into the water which fills the reactor pressure vessel and surrounding reactor cavity.
2. Description of the Relevant Art
Movement of large pieces of equipment and components of a boiling water reactor is accomplished by flooding the reactor cavity and pressure vessel in a manner wherein radioactive emissions are suppressed and it is possible to remove the reactor head and perform routine maintenance, refuelling and the like. These procedures however, require that large pieces of equipment, such as a steam seperator, be lifted out of the reactor pressure vessel and transferred to pools which are provided adjacent to the vessel and that form part of the reactor cavity. To achieve this transfer, it is necessary to use a heavy-duty overhead crane which comprises a part of the reactor system and which is mounted above the reactor cavity. Due to the limited space available within the reactor pressure vessel and the geometry of the pool of the reactor cavity within which the loads are temporarily stored, it is sometimes necessary to lower the crane hook below the surface of the water. Because the water is radioactive, it is undesirable for the crane hook, hook block or cables which support the hook block, to come into direct contact with the water, as such contact causes contamination and demands that these pieces of apparatus be thoroughly washed or otherwise suitably decontaminated after use.
U.S. Pat. No. 5,170,899 issued on Dec. 15, 1992 in the name of Baversten (one of the two inventors named on this application), discloses an arrangement wherein a telescopic cover arrangement is provided on the hook box connected to the load to be lifted by the crane. The telescopic arrangement is arranged to be extendible when the hook is lowered below the surface of the water in a manner which encloses the hook, hook block and the lower portions of the suspending cables and provides an air space thereabout. However, in order for this telescopic arrangement to be effective, a water-tight interface must be provided between the two moving elements. Further, in order achieve extension and contraction of the arrangement a remotely controlled servo which is either hydraulic or pneumatically operated, is required. This construction, however, requires both a precise seal and the provision of the remotely controlled hydraulic or pneumatic servo. The construction is thus relatively complex and expensive.